Previous deafferentation experiments from this laboratory have been addressed to the task of determining whether somatic sensation, and sensory feedback in general, is necessary for various types of learning and for the performance of different categories of movement. We have shown that monkeys are capable of making much greater use of limbs from which sensation has been abolished by dorsal rhizotomy than had previously been thought possible. The present project has been designed with two general purposes in mind. In Study Area I, an attempt is being made to define quantitatively the deficit in movement and learning produced by brachial dorsal rhizotomy. Currently we are studying prehension and ambulation. In the future we will be studying ability to cross horizontal planks and ladders of different sizes, jumping, vertical climbing, lateral climbing, force regulation, and certain types of serial behavior. Study Area II represents an attempt to determine the neural and restitutive mechanisms that make it possible for monkeys to make effective use of deafferented limbs, even when vision is occluded (e.g., central feedback pathways, collateral intraspinal sprouting).